A cable used for the USB standard (USB cable) has four electric wires including a pair of differential data lines, a power line, and a ground line. Generally, a shield layer braided with a copper wire is provided in order to suppress noise emission from the cable to the outside and entrance of an electromagnetic wave from the outside to the inside. The shield layer has both end portions each connected to a ground potential portion.
However, in the case where the ground potential is not ensured, there may be a problem in which an electromagnetic shielding effect becomes insufficient. Furthermore, in the case where ground potential of two apparatuses to be connected are not equal, there may be a problem in which current flows via the shield layer and noise is transmitted to the apparatuses. Additionally, there are proposed measures against such problems, in which noise is suppressed by using a resin obtained by mixing a coating material to coat the shield layer with an electric wave absorbing material such as ferrite. Furthermore, the measures are taken by providing a noise suppressing member such as an inductance at a connecting portion of a cable connected to an apparatus.
For example, Patent Document 1 discloses, in FIG. 2, a structure in which a conductor 1 includes a plurality of insulating electric wires 3 coated with an insulating body 2, a braided copper 4 is wound around the outside thereof, additionally a sheath 5 made of an insulating material is disposed outside thereof, and a ferrite-containing resin 6 is provided between the insulating electric wire 3 and the braided copper 4. Such a cable disclosed in Patent Document 1 can reduce noise of a high frequency zone (10 kHz to 1 GHz) by the braided copper 4, can suppress noise (1 kHz to 10 kHz) by ferrite powder contained in the insulating body 2, and can reduce noise of a lower frequency zone by the ferrite-containing resin 6.
Patent Document 2 states that: the technology disclosed in Patent Document 1 includes the shield layer, and when the shield layer is not surely connected to reference potential, there may be a problem in which EMI noise is emitted to the outside from the shield layer.